1. Field of the Invention
The present invention relates generally to apparatuses and methods for optical coherence tomography, and more specifically to apparatuses and methods for providing improved optical coherence tomography images.
2. Description of the Related Art
Optical coherence tomography (OCT) is widely used in medicine to image tissues of various part of the body. See, e.g., T. Asakura, “International trends in optics and photonics ICO IV,” (Springer-Verlag, Berlin Heidelberg, 1999) pp. 359-389; D. Huang, et al. “Optical coherence tomography,” Science, Vol. 254, pp. 1178-1181 (1991); J. G. Fujimoto, et al. “Optical biopsy and imaging using optical coherence tomography,” Nature Medicine, Vol. 1, pp. 970-972 (1995); A. F. Fercher, C. K. Hitzenberger, G. Kamp, and S. Y. El-Zaiat, “Measurement of intraocular distances by backscattering spectral interferometry,” Opt. Commun., Vol. 117, pp. 43-48 (1995); G. Hausler and M. W. Lindler, “Coherence radar and spectral radar-New tools for dermatological diagnosis,” J. Biomed. Opt., Vol. 3, pp. 21-31 (1998); M. Wojtkowski, R. A. Leitgeb, A. Kowalczyk, T. Bajraszewski, and A. F. Fercher, “In vivo human retinal imaging by Fourier domain optical coherence tomography”, J. Biomed. Opt., Vol. 7, pp. 457-463 (2003); R. A. Leitgeb, C. K. Hitzenberger, and A. F. Fercher, “Performance of Fourier domain vs. time domain optical coherence tomography,” Optics Express, Vol. 11, pp. 889-894 (2003); M. A. Choma, M. V. Sarunic, C. Yang, and J. A. Izatt, “Sensitivity advantage of swept source and Fourier domain optical coherence tomography,” Optics Express, Vol. 11, pp. 2183-2189 (2003); R. A. Leitgeb, C. K. Hitzenberger, A. F. Fercher, and T. Bajraszewski, “Phase-shifting algorithm to achieve high-speed long-depth-range probing by frequency domain optical coherence tomography,” Opt. Lett., Vol. 28, pp. 2201-2203 (2003); R. A. Leitgeb et al. “Ultrahigh resolution Fourier domain optical coherence tomography,” Optics Express, Vol. 12, pp. 2156-2165 (2004).
FIGS. 1A and 1B schematically illustrate two OCT configurations for use with the two major techniques of OCT, time-domain OCT and frequency-domain OCT, respectively. In both time-domain OCT and frequency-domain OCT, a broadband light source 10, such as a superluminescent diode, a mode-locked laser, or even a supercontinuum generating fiber, feeds an interferometer 20, typically a Michelson interferometer. A reference broadband mirror 30 is placed on one arm of the interferometer 20, and the tissue 40 is on the other arm of the interferometer. In the OCT configurations of FIGS. 1A and 1B, the light source is split into two fields using a beam splitter 50 or a fiber coupler (FC), and each field is directed towards one arm of the interferometer 20. The reflected light from the tissue 40 and from the reference mirror 30 are combined collinearly at the detector 60. The basic difference between time-domain OCT and frequency-domain OCT is that in time-domain OCT, the reference mirror 30 is a movable mirror, which is scanned as a function of time during the image acquisition. However, in the frequency-domain OCT, there are no moving parts, and at the detector end, the spectrum of the interference between the two reflected signals coming from each arm of the interferometer is recorded by means of an optical spectrum analyzer (OSA), e.g., a charged-coupled-device (CCD) array with the appropriate imaging optics. There are significant advantages of frequency-domain OCT over time-domain OCT, such as higher speed and higher sensitivity.